Satellites employed in satellite communication systems typically must communicate with multiple users simultaneously. Typical methods for multiplexing multiple users are TDMA, FDMA, and CDMA.
CDMA, or Code Division Multiple Access, allows for multiple users through the use of spread spectrum techniques which assign different spreading codes to different users. If all the spreading codes are perfectly orthogonal, then when each user de-spreads his signal using his code, there is no interference contributed by the other users' signals. In practice, pseudo-random spreading codes are used, which are not completely orthogonal. Because of the non-orthogonality of commonly used spreading codes, or otherwise imperfect synchronization with orthogonal codes, multiple users in a satellite communication system employing CDMA necessarily cause interference in each other's communications.
As the number of users communicating with a single satellite increases, the interference increases and the quality of communication drops. The quality of communications and the capacity of the system, as measured by the number of possible simultaneous users, are important performance measures of a satellite based communication system.
Accordingly, there is a great need for a system and method for reducing the interference between users and thus increasing the available capacity of the system and improving the quality of communications.